Padmashri Ragunathan, Ganguly Archan, Mondal Partha Pratim, Rajan K, Sikdar Sujit Kumar
Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India.
Cell Calcium. 2006 Mar;39(3):247-58. doi: 10.1016/j.ceca.2005.11.003. Epub 2005 Dec 27.
It is not clear how different spatial compartments in the neuron are affected during epileptiform activity. In the present study we have examined the spatial and temporal profiles of depolarization induced changes in the intracellular Ca(2+) concentration in the dendrites of cultured autaptic hippocampal pyramidal neurons rendered epileptic experimentally by treatment with kynurenate (2 mM) and Mg(2+) (11.3 mM) in culture (treated neurons). This was examined with simultaneous somatic patch-pipette recording and Ca(2+) imaging experiments using the Ca(2+) indicator Oregon Green 488 BAPTA-1. Neurons stimulated by depolarization under whole-cell voltage clamp conditions revealed Ca(2+) entry at localized sites in the dendrites. Ca(2+) transients were observed even in the presence of NMDA and AMPA receptor antagonists suggesting that the opening of voltage gated calcium channels primarily triggered the local Ca(2+) changes. Peak Ca(2+) transients in the dendrites of treated neurons were larger compared to the signals recorded from the control neurons. Dendritic Ca(2+) transients in treated neurons showed a distance dependent scaling. Estimation of dendritic local Ca(2+) diffusion coefficients indicated higher values in the treated neurons and a higher availability of free Ca(2+). Simulation studies of Ca(2+) dynamics in these localized dendritic compartments indicate that local Ca(2+) buffering and removal mechanisms may be affected in treated neurons. Our studies indicate that small dendritic compartments are rendered more vulnerable to changes in intracellular Ca(2+) following induction of epileptiform activity. This can have important cellular consequences including local membrane excitability through mechanisms that remain to be elucidated.
目前尚不清楚在癫痫样活动期间神经元内不同的空间区室是如何受到影响的。在本研究中，我们检测了通过在培养物中用犬尿氨酸（2 mM）和镁离子（11.3 mM）处理而实验性诱发癫痫的培养自突触海马锥体神经元树突中，去极化诱导的细胞内钙离子浓度变化的空间和时间特征。这是通过使用钙离子指示剂 Oregon Green 488 BAPTA-1 的体细胞膜片钳记录和钙离子成像实验同时进行检测的。在全细胞膜片钳条件下去极化刺激的神经元在树突的局部位点显示钙离子内流。即使在存在 NMDA 和 AMPA 受体拮抗剂的情况下也观察到钙离子瞬变，这表明电压门控钙通道的开放主要触发了局部钙离子变化。与对照神经元记录的信号相比，处理过的神经元树突中的钙离子瞬变峰值更大。处理过的神经元中的树突钙离子瞬变表现出距离依赖性缩放。树突局部钙离子扩散系数的估计表明处理过的神经元中的值更高，并且游离钙离子的可用性更高。对这些局部树突区室中钙离子动力学的模拟研究表明，处理过的神经元中局部钙离子缓冲和清除机制可能受到影响。我们的研究表明，在诱发癫痫样活动后，小的树突区室变得更容易受到细胞内钙离子变化的影响。这可能会产生重要的细胞后果，包括通过尚待阐明的机制导致局部膜兴奋性改变。
